Mitofusin 2 (MFN2) is a mitochondrial transmembrane GTPase regulating mitochondrial fusion and that the nucleotide-dependent activation of MFN2 concomitantly protects the organelle from permeability transition. It is mapped to chromosome 1 and encodes a 757-amino acid protein that contains an ATP/GTP-binding site motif. It is expressed in many tissues and cell lines such as brain and KG-1 with the highest expression in heart and skeletal muscle. This protein contains an N-terminal GTPase domain and a transmembrane domain near the C terminus. It shares 60% identity with MFN1. When stably expressed in COS-7 cells, MFN2 colocalizes with mitochondrial markers. Axonal CMT type 2A and autosomal dominant HMSN VI are caused by MFN2 and mutations in MFN2, which emphasizes its important role of mitochondrial function for both optic atrophies and peripheral neuropathies.